Sodium

Na⁺ 135-145 meg/L

• H₂O – 60% male, 50% female
• TBW – 1/3 ECF (1/4 IV, ¾ IS) , 2/3 ICF
• 85-90% of total body Na⁺ is extracellular (95% K⁺ is intracellular)

ECF Volume

• Depletion: deficit in total body Na⁺ (renal or extrarenal loss > Na intake)
• Expansion: salt intake with renal Na⁺ retention (renal disorder or 2^O to decrease effective circulating volume – HF or hypoalbumin)

Hyponatremia

• Isotonic → hyperlipidemia, hyperprotenemia; no change in osmolarity; ↓ H₂O volume so that ↓[Na] in plasma volume (pseudo!)
• Hypertonic → hyperglycemia; ↑ glucose draws H₂O into EC space from cells
• Hypotonic → assess volume status (clinically)
  • Hypovolemic:
    • Extrarenal salt loss (GI)
    • Renal salt loss (diuretics, ACEi, mineralocorticoid deficiency, etc.)
  • Euvolemic:
    • SIADH (↓Na, ↓urea, ↓plasma osmolarity, ↑urine osmolarity)
    • Psychogenic polydipsia
    • Asymptomatic
      • H₂O restric
      • 0.9% NS and furosemid
      • Demeclocycline – inhibit AD
    • Symptomatic
      • Saline 3% and furosemid
    • Watch out for central pontine myelinolysis if corrected too fast (1-2 meq/L/h
  • Hypervolemic: edema associated disease
    • Treatment – H₂O restrict and diuretics

Hypernatremia

• Concentrated urine (urine osmolarity > 400 mosm/kg)
  • • renal H₂O conserving function norma
  • Non-renal loss (sweat, respiratory, stool)
  • Renal loss (osmotic diuresis – glycosuria, mannitol, urea
• Dilute urine (urine osmolarity < 250 mosm/kg)
  • Central DI
  • Renal insensitivity to ADH
    • Nephrogenic (Li or demeclocycline) DI
    • Relief of urinary tract obstruction
    • Nephritis